1. Field of the Invention
The present invention relates to a sealed semiconductor device and a method of manufacturing the semiconductor device.
2. Description of the Related Art
In recently years, as the technology develops, semiconductor devices utilizing a wiring board have been put into practical use. Conventionally, BGA (Ball Grid Array) type semiconductor devices are known. The BGA type semiconductor device comprises a wiring board for mounting a semiconductor chip, wires for connecting the wiring board and the semiconductor chip, sealing resin for protecting the semiconductor chip from the outer environment, and a solder ball as an external terminal.
The BGA type semiconductor devices are manufactured as follows. First, a semiconductor chip is mounted on a single wiring board of an integral molding type, and next the semiconductor chip and the wiring board are connected by wires made of materials such as gold (Au). Then, a sealing part is formed by an integral molding method, thereafter solder balls are mounted, and finally the wiring board is cut along the external shape of the semiconductor device.
In a BGA (Ball Grid Array) type semiconductor device which adopts the above-mentioned method of forming a sealing part in an integral manner, there is a difference in the thermal expansion coefficients between the sealing resin that is formed to cover the semiconductor chip on the wiring board and the wiring board. As a result, when subjected to a sealing step involving heat generation, the wiring board will exhibit warping. When such warping of the wiring board is large, handling and positioning of the wiring board will become difficult in the manufacturing process of the semiconductor device. Therefore, there is the problem in which productivity in manufacturing a semiconductor device declines.
Techniques to solve such warping of the wiring board include a method to divide the sealing part into two or more sections (see Japanese Published Unexamined Patent Application No. 2001-44324). Dividing the sealing part into two or more sections will lessen the warping of the wiring board compared with the case in which the sealing part is in a single section.
Even when the sealing part is divided into two or more sections, the sealing part is formed across the wiring board when viewed as a unit product. Therefore, the problem of warping of the wiring board will be caused when the area of the sealing part is large. The larger the area of the wiring board, the larger is the warping of the wiring board.
Further, the warping of the wiring board can be lessened by dividing the sealing part further into more sections; however, in such a case, the region of the wiring board where the sealing part is not formed will increase. The region where the sealing part is not formed is a portion at which the upper and lower molding dies are brought into contact when applying resin sealing. That is, the product can not be formed in the region. Therefore, the number of semiconductor devices formed from one wiring board will be decreased. Such decrease in the number of semiconductor devices produced from a single wiring board will result in an increase in the manufacturing cost of semiconductor device.